The present invention relates generally to pistons for internal combustion engines, and more specifically, to a piston having a uniquely shaped recess formed in the combustion face of the piston.
In general, fuel injected engines include multiple cylinders that receive an atomized fuel injected into the cylinder. The fuel injector provides a fine mist of fuel that mixes with combustion generating gases, generally a mixture of fresh air and any remaining exhaust gases, within the cylinder. This mixture is then compressed and either spark ignited in gasoline engines, or compression ignited in diesel engines. While diesel engines may realize benefits from the present invention, it is primarily directed to fuel injected, spark ignited engines.
In this category of engines, the present invention is applicable to both two-cycle and four-cycle engines. Two-cycle engines are those engines that produce a power stroke with every rotation of the crank shaft. Direct fuel injected engines are those having a fuel injector arranged to inject fuel directly into the cylinder as opposed to port fuel injected engines that mix air and fuel before entry into the cylinder. Two-stroke engines, by nature, are more prone to high exhaust emissions. The two-stroke engine industry, if it is to survive, must maximize efficiency and minimize the emissions to comply with governmental regulations. In the last few years, many advances have been made to advance two-stroke engines toward these goals. Since two-stroke engines are significantly lighter in weight than four-stroke engines, they have a distinct advantage. Recently two-stroke engines manufactured by the Assignee of the present invention have resolved fuel efficiency concerns and reduced emissions to levels unheard of just a few years ago. Two-stroke engines now hold a distinct advantage over four-stroke engines. However, further advancement is desirable to further increase the desirability of two-stroke engines over four-stroke engines in various applications, such as those described above. Two-cycle engines that employ direct fuel injection will receive the most beneficial results with use of the present invention, however, other engines may benefit as well.
In order to improve the combustion process and reduce emission in the exhaust gases, it is desirable to obtain effective mixing and atomization of the fuel within the cylinder space. In so doing, it is desirable to prevent fuel from being accumulated on any surfaces of the combustion chamber. These surfaces include the face of the piston, the cylinder walls, and the area of the cylinder head enclosing the combustion chamber. Fuel accumulated on these surfaces is generally more difficult to ignite than atomized fuel mixed with air.
Fuel injected into the combustion chamber that is not thoroughly atomized and dispersed within the combustion chamber can create areas of uneven combustion. Areas of the combustion mixture having too little fuel lead to a lean burn and areas having too much fuel result in a rich burn. It is widely known that lean and rich burning combustion results in higher levels of pollutants in the exhaust gas as compared to the level of pollutants generated from a burn that is more fully atomized and dispersed within the spark zone.
Additionally, regions of high fuel concentration require more time for the fuel to burn as compared to areas where the fuel concentration is not as high. Often this time delay allows the temperature in the cylinder to drop to a point where the fuel is not readily burned. This type of uneven burning, as discussed above, leads to increased hydrocarbon and soot emissions from the engine. As such, it is important that the fuel injected into the combustion chamber not form regions of high concentration within the mixture.
Also, the surface temperatures of the combustion chamber can negatively effect fuel atomization. The combustion face of the piston, the portion of the cylinder wall within the combustion chamber, and the cylinder head surface enclosing the combustion chamber are generally at a temperature lower than the temperature of the burning fuel/air mixture. This results in a lower temperature burn of the atomized fuel that is in close proximity to these surfaces during the combustion process.
Some prior art diesel pistons include a recess in the piston that is designed to retain fuel for compressive combustion within the bowl. Others have designed the bowl as a means for cooling the head of the piston. Some gasoline-type engines have recesses that are configured to provide clearance for the valves of a four-stroke engine. In other gasoline engines, in order to minimize cylinder head dimensions, the spark plug and fuel injector enter the cylinder from opposite ends, and in these arrangements, the recess is designed to reflect fuel entering the recess from an angle, and redirect the fuel toward the spark plug. These prior art configurations are not very effective at redirecting fuel to maximize efficiency and minimize emissions in two-stroke engines where the fuel injector is located such that the fuel spray is directed nearly vertically and where it is desired that the fuel be redirected generally back toward the fuel injector.
It would therefore be desirable to have an engine with a cylinder arrangement that could receive a fuel mixture from a fuel injector and both provide a thorough mixture of atomized and combustion gas, and direct that mixture toward a preferred combustion area while preventing accumulation of the mixture near the interior surfaces of the combustion chamber.